For commercial air travel, an efficiently and effectively operating toilet system must be maintained for the convenience and well-being of the passengers and crew. With current aircraft design, waste from the toilet system is stored on board in one or more holding tanks for the duration of the flight. Over the course of a nine to eleven hour international flight with a wide-body airplane such as one of the Boeing 747 models, it is not unusual for as much as 2500 pounds of waste water to accumulate in the holding tanks. With narrow-body aircraft such as a Boeing 727 model, in excess of 800 pounds of waste water can be accumulated.
Occasionally, the toilet system will fill to capacity, causing the system to be closed and unusable for a portion of the flight. Additionally, even if the holding tanks do not reach capacity, frequently there will be sufficient accumulation to produce objectionable odors which will be picked up by the plane's ventilation system and carried throughout the cabin.
These problems have been exacerbated over the past several years due to the increased competition in air travel. To reduce cost and improve competitiveness, many airlines have increased the number of seats in each plane and, on shorter flights, do not empty the holding tanks each time that the plane lands. The additional weight thus carried also results in increased consumption of fuel, in turn adding to the overall cost for the airlines to do business.
To minimize the waste water that must be stored during flight, a variety of systems have been developed to re-use the waste water to provide the water necessary to operate the aircraft toilet system. For example, U.S. Pat. No. 3,995,328, "Vacuum Toilet System", describes a recirculating vacuum toilet system in which water is recovered from the toilet waste and recycled as rinsing fluid to clean the toilet bowl. Vacuum toilet systems have also been developed in which untreated "grey" water from sinks and galleys on the aircraft is used as toilet rinse water. U.S. Pat. No. 5,454,936, "Vacuum Toilet System" thus describes a system in which the grey water is collected from the lavatory sinks in a secondary tank and thereafter delivered as rinse water for the toilets. In both of these systems, however, the waste water must still be stored on board the aircraft and consequently, neither system provides a satisfactory solution to the problems confronting the airline industry.
A system has also been described for dehydrating aircraft waste water and discharging or re-using the water, U.S. Pat. No. 5,080,797, "Method of Disposing of Fecal Matter From Toilet Systems In Fast Moving Vehicles". This system, however, proposes to use a pump to force contaminated waste water through a heated dehydration tank, and thus represents an approach that is impractical to employ in commercial aviation, in view of the high levels of energy that would be required and safety concerns due to the potential for overheating.
Untreated grey water from the sinks and galleys of the aircraft, if not recirculated as toilet rinse water, is discharged to the external atmosphere during flight through the drain mast of the plane, using the pressure differential between the cabin pressure of the aircraft and the external atmosphere. If this water is used to rinse the toilets, however, it must be stored on board the aircraft, because the level of contamination exceeds the regulatory standards for water that may be discharged to the atmosphere. While the use of sink water thus offers a cleaner and more appealing rinse water for the aircraft toilet system than re-use of toilet waste water, it does not represent a satisfactory solution.
It would be highly advantageous, therefore, if the toilet waste water, including recirculated waste water from the sinks and galleys, could be decontaminated in flight to a level sufficient to permit it to be discharged to the atmosphere. It is accordingly a principal object of the present invention to provide a method and system for treating aircraft waste water to remove contaminants and discharge the treated water to the atmosphere during flight.